Flyback Driver Circuit with 2N3055
This is probably the most well known flyback transformer driver circuit. It uses two 2N3055 power transistors in a push-pull oscillator configuration. The value of the resistors is not that critical. In fact you can even use a 1/2W for the 27 ohm resistor, but it may burn out if it is left to run for a long time. This circuit will accept voltages up to about 24V, but I would not go any above this as you risk destroying the flyback transformer. Try to find an old flyback. It should have a rather disk shaped high voltage winding, rather than a cylindrical one. Also it should not have a rectifer built in. The rectifer decreases the performance of this circuit greatly since it cuts off the other cycle. You should not run this on any power supply which is expensive. Link
Other Link
LM317T Voltage Regulator with Pass Transistor
12V 50W AC-DC Power Supply
10-30kV TV flyback driver with 2N3055
High voltage spill equal DC 900V
High Voltage mini power supply by 2N2222
